Faujasite supercage with copper ions occupying 6-ring windows
sites (A); ó-donation of ð-electrons of thiophene to the 4s orbital of copper-
(I) (B); d-ð* back-donation of electrons from 3d orbitals of copper(I) to
ð* orbitals of thiophene. Here 3d represents dxy, dyz, or dxz, or 3 of the 5 3d
orbitals.